docs: include allowed file extensions to upload in `ui` #154

Job	Run time
contract-call-decoder unit tests	3m 20s
lib-sourcify unit tests	4m 8s
server over Ganache integration tests	4m 56s
server over Hedera's local node integration tests	5m 2s
bytecode-utils unit tests	2m 46s
	20m 12s

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